Process of making plug gauges



May 27, 1941.

W. T. SCHAURTE PROCESS OF MAKING PLUG GAUGES Filed Aug. 2, 1939 ATTORNEYS Patented May 27, 1941 PROCESS OF MAKING PLUG GAUGES Werner T. Schaurte, Lauvenburg, near Neus Germany Application August a, 1939, Serial No. 287,969

4 Claims.

This invention relates to a process of making plug screw thread gauges, either working or reference gauges.

Gauges of this type have been made heretofore by turning out a suitable blank from a tool steel rod, milling or rough turning the threads, hardening the material and then grinding and lapping the threads to size. These operations, however, require annealing prior to the machining operations and ordinarily a second annealing after the rough turning and before the cutting of the threads. In order to obtain a harder and more corrosion resistant and accurate surface on the threads of the gauge it has also been proposed to plate the gauge threads with chromium. Gauges have been made in this manner heretofore by annealing the stock, turning out the blank, milling or turning the threads, rough grinding, hardening, and chromium plating the threads, followed by further grinding operations and finishing with a lapping operation to bring the threads to the exact size desired.

All of the prior methods of making such gauges have been quite costly, since they require at least one and usually two annealing operations and a hardening operation in addition to the relatively slow turning and thread cutting operations. In addition when it has been attempted to' chromium plate the threads it is found that a greater thickness of chromium is deposited at the roots of the threads than at the tops of the threads. As a consequence it is necessary to out the threads with a slightly smaller angle between the sides of each thread and slightly greater depth than is desired for the finished gauge, allowing the threads to be brought to the desired angle and depth by the excess of chromium deposited at the roots of the threads. The chromium surfaces of the threads must then be finished by rough grinding, finish'grinding and lapping.

I have discovered that accurate and durable gauges of this type may be rapidly produced at but a fraction of the cost of gauges made by the prior art methods by simply grinding a steel bar of suitable hardness, chromium plating the bar, rolling the desired threads upon the chromium plated surface and finishing the threads to exact size by lapping. The same operations, omitting the chromium plating, may be used where it is desired to produce gauges of the older type in which the thread surfaces are not plated. The remainder of the bar which does not carry the threads may be inserted directly into a suitable handle or, if desired, reduced and tapered in acished gauge, the thickness of the chromium plating again being slightly exaggerated.

In carrying out my process I preferably start with a bar 5 as illustrated in Figure 1 of hardened tool steel or of a steel which does not require a separate hardening step such, for example, as cold drawn manganese steel. The bar is first reduced to uniform cylindrical size and provided with a suitably finished surface by centerless grinding. If a reduced or tapered portion to be inserted in and secured to a handle is desired, this portion may be turned down prior to grinding.

After being ground the bar is plated with a hard, thin and tenacious film 6 of chromium in accordance with any suitable process. The proc ess should be such as to produce a relatively thin and uniformly adherent coating in order that it will not crack or separate from the steel during subsequent operations.

The plated bar is then passed between thread rolling dies "by means of which a thread 1 of the desired dimensions with an allowance of a few thousandths of an inch for finish lapping is formed on a portion of the bar. Since the thread roiling operation involves a displacement as dis-- tinguished from a cutting of the material thetops 8 of the threads extend beyond the original diameter of the stock and the root portions 9 are depressed a correspondingamount within the original diameter. This displacement of the metal requires a corresponding displacement of the chromium filmG so that each side of each thread contains a roughly frusto-conical chromium layer which has been formed by expanding one side and correspondingly reducing the opposite side of an initially cylindrical portion of the plate. However, this does not result in thickening the chromium at the roots of the threads and thinning it at the tops because the projections upon the thread rolling dies initially engage the stock at the points which ultimately become the root portions of the thread and the tops of the threads are engaged by the dies only when the thread has been completely formed so that the greatest amount of pressure and working occurs at the roots of the threads, thereby maintaining the film of chromium substantially uniform in thickness.

The carrying out of the thread rolling process upon the relatively hard material of the gauge requires only a thread rolling mechanism of sufficient rigidity so that the dies are not sprung apart or misaligned appreciably by the pressures developed in the rolling operation. Such rigidity is easily obtained by simply using an over-size thread rolling machine, or one intended for rolling threads upon stock of larger diameter than the stock of the gauge being produced. A standard reciprocating thread rolling machine is preferred for this operation.

It is characteristic of .the thread rolling process that perfect threads may be produced to a much smaller tolerance than is possible by cutting or milling operations. As a consequence following the rolling of the threads on the gauge it is only necessary to finish the threads by a lapping operation with the removal of only a very slight amount of material. In this way I am enabled by the present process to eliminate not only the expensive annealing and machining steps of the prior processes, but also the relatively expensive grinding of the threads. As a consequence I am able to produce accurate and durable gauges equally as good as those produced by the prior art process at a fraction of the cost aeaaeoe involved in the prior art processes. It will, of course, be understood that where it is desired t produce the older form of gauge in which the surfaces of the threads are not plated, I can carry out the same process with the omission of the step of chromium plating and realize an equivalent saving in cost over the prior processes of making unplated gauges.

I claim:

1. The process of making screw thread gauges of the plug type comprising grinding a cylindrical piece of steel, plating the surface of the ground piece with chromium, and rolling a thread upon the plated piece.

2. The process of making screw thread gauges of the plug type comprising grinding a cylindrical piece of hard steel, plating the ground piece with chromium, rolling a thread upon the plated surface and finishing the thread by lapping.

3. The process of making screw thread gauges of the plug type comprising plating the surface of a cylindrical pieceof steel with chromium and rolling a thread upon the plated piece.

4. The process of making screw thread gauges of the plug type comprising plating the surface of a cylindrical piece of steel with chromium, rolling a thread upon the plated piece and finishing the thread by lapping.

WERNER T. SCHAURTE. 

